This invention relates to apparatus for converting the optical image of a laboratory slide to electrical signals and more particularly to an automatic focusing system for such apparatus.
In the analysis of blood samples, the blood is smeared on a laboratory slide and the smear is stained. By counting the different kinds of leukocytes on the stained smear, laboratory technicians perform what is referred to as a white blood cell differential. Automation of this differential has significant economic impact because the differential is performed so frequently at every hospital. A thesis by J. W. Bacus, "An Automated Classification of the Peripheral Blood Leukocytes by Means of Digital Image Processing", University of Illinois, Chicago, 1971, describes one automated system.
In a system developed by my co-employees, a scanning unit (in this case a T.V. camera) linearly sweeps a vidicon target subjected to intense illumination which passes through the smeared slide. Such a system is described in copending application Ser. No. 353,004, filed Apr. 20, 1973 now U.S. Pat. No. 3,883,852.
In such a system the light passing through the slide is focused by an objective lens. It is desirable to bring this image into focus on the television type converter.